> -----Original Message----- > From: Markus Lindholm [mailto:[email protected]] > Sent: 20 August 2012 11:51 > To: Tag discussion, strategy and related tools > Subject: Re: [Tagging] Carriageway divider > > On 20 August 2012 10:55, Gregory Williams > <[email protected]> wrote: > >> -----Original Message----- > >> From: Markus Lindholm [mailto:[email protected]] > >> Sent: 19 August 2012 19:26 > >> To: Tag discussion, strategy and related tools > >> Subject: Re: [Tagging] Carriageway divider > >> > >> On 19 August 2012 18:23, Tobias Knerr <[email protected]> wrote: > >> > On 19.08.2012 15:09, Markus Lindholm wrote: > >> >> On 19 August 2012 14:49, Fabrizio Carrai > >> >> <[email protected]> > >> wrote: > >> >>> This could be a solution but it is against the reality: this kind > >> >>> of road are indeed a single entity. The "legal" division, i.e. > >> >>> the "solid_line" is just an attribute. > >> >> > >> >> There's a multitude of cases where a single entity is represented > >> >> by multiple objects in the database, e.g. when the road changes > >> >> speed limit it has to be split into two highway objects. The same > >> >> with bus routes, to accommodate then the road was to be split into > many parts. > >> > > >> > A major difference is that it is comparatively easy to re-assemble > >> > a way that has been split (because they have common nodes). > >> > > >> > It's not so easy with two parallel ways that somehow "belong together" > >> > - the connection could only be established by rather complex > >> > heuristics based on proximity among other things. In practice, it > >> > would simply result in gaps or overlaps appearing randomly > >> > depending how > >> "parallel" > >> > the mapper has actually drawn the ways, and on the width assumed > >> > (or > >> > tagged) for the ways. > >> > >> For which purpose would the two highways be "reassembled"? > > > > Split highways may be reassembled when you're not interested in the > > attributes that do change between them. For example when you want to > > reassemble the portions of the same road with the same class and name > > together but aren't interested in the fact that the speed limit > > changes partway down, the lighting changes, the surface changes, or > > that a small portion of it has a cycle or bus route which crosses it > > for a few tens of metres. If building a routing graph from the data > > you'd want to keep the graph as simple as possible by ignoring the > > tags not relevant to your routing and reassembling the adjacent otherwise > identical segments. > > Yes, I understand why one would reassemble highway segments on a route > that only differ on the maxspeed tag or other such minor issue. But why > would one want to reassemble two highways going in opposite direction and > from which there is no direct legal route to the other? > > /Markus
Most of this still applies to two parallel opposite highways. When building a routing graph you may want to combine the opposing ways together into one way that represents both directions in order to simplify the routing graph. _______________________________________________ Tagging mailing list [email protected] http://lists.openstreetmap.org/listinfo/tagging
